Magnetic reading and writing device

ABSTRACT

In a magnetic reading/writing device, a controller derives at each radius of a recording medium a slope of a curve of track-averaged write performance with respect to an adjustment parameter, and determines a first set of fitting coefficients of a first equation approximating the derived slopes in terms of a first variable representing each radius. The controller acquires write performance dependence on a variable representing each of multiple circumferential positions of the medium by measuring track average write performance with respect to the circumferential positions, and determines a second set of fitting coefficients to approximate by a periodic function the acquired dependence in terms of the first variable. The controller corrects a condition value representing the adjustment parameter by subtracting from the condition value an adjustment value obtained from functions calculated with the first and second sets of fitting coefficients.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 13/271,176,filed Oct. 11, 2011, and claims priority under 35 U.S.C. §119 fromJapanese Patent Application 2011-001336, filed Jan. 6, 2011, theentirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a magnetic reading and writing device and acontroller of the device.

2. Description of the Related Art

In current hard disk drives, in order to raise recording densities tothe extent possible and realize large recording capacities for specificcombinations of magnetic reading and writing heads and a magneticrecording medium, processing has been performed to optimize therecording current and track density, as well as the heater power forcontrol of the flying height of the magnetic reading and writing heads.Optimum conditions differ depending on the radius, due to thecircumferential speed dependence and skew dependence of the head flyingcharacteristics, as well as the radial dependence of the magneticcharacteristics of the magnetic recording medium. Hence, in general,optimization processing depending on the radius has been performed in amagnetic recording system. Specifically, the write current, distancebetween tracks (hereafter called the “track pitch”), linear recordingdensity, as well as the heater power for the flying height control areselected so as to maximize the recording density at each radius, as aresult of which drive storage capacity is optimized.

Japanese Patent Application Laid-open No. H8-45007 discloses a magneticdisk device which performs correction of writing signals and reproducedwaveforms is disclosed. In the magnetic disk device, when data isreceived from a higher-level device during operation, a recording systemconverts the data into recording signals and outputs the signals to themagnetic head, thereby recording the recording signals on the magneticdisk. At this time, a preshifter performs correction such as delayingthe recording signals. The correction amount in this case is calculatedby recording correction amount calculation means based on the peakposition of a reproduced waveform. On the other hand, a reading systemof the device converts readout waveforms read by the magnetic head fromthe magnetic disk into data, and outputs the data to a higher-leveldevice. At this time, the filter corrects the amplitude and similar ofthe readout waveforms. The correction amount in this case is calculatedby read/write correction amount calculation means, based on the pulsewidth of the readout waveforms (see paragraphs [0008] and [0009] ofJapanese Patent Application Laid-open No. H8-45007). In accordance withthis device, by calculating a correction amount in advance for eachtrack, the correction amount which absorbs scattering at the time ofmagnetic disk manufacture and the like can be calculated (see paragraphs[0021], [0026] and [0027], and similar of Japanese Patent ApplicationLaid-open No. H8-45007).

Further, Japanese Patent Application Laid-open No. 2009-129532 disclosesa mechanism which, in order to compensate readout signal output, uses aheater for control of the flying height of a magnetic read/write head.

In an actual magnetic recording medium, there are cases in which thereis a gentle characteristic distribution not only in the radialdirection, but in the circumferential direction as well. If reading andwriting optimization processing is performed using such a magneticrecording medium with a dependence only on the radial direction, as inthe prior art, then it is possible that the recording capacity will begreatly inferior to what should in principle be obtained when performingoptimization which includes a dependence on the circumferential positionas well. In particular, where the write performance is concerned, whenthere is unevenness in the circumferential position, under constantconditions in the circumferential position, the write width is broad inportions where the write performance is high and the track pitch cannotbe narrowed. Conversely, in portions where the write performance is low,under conditions optimized for portions with high write performance,there is the concern that write performance will be inadequate.

SUMMARY OF THE INVENTION

This invention was devised in light of the above problems, and has as anobject the provision of a magnetic reading and writing device which canperform reading and writing optimization processing which depends on thecircumferential position as well, without requiring the addition ofconsiderable resources compared with conventional optimization methods.

In order to attain the above object, a first mode of the invention is amagnetic reading and writing device, which includes a magnetic head, amagnetic recording medium, nonvolatile memory, and a controller. Themagnetic head has a magnetic read/write function and a flying heightcontrol function. On and from the magnetic recording medium, reading andwriting are performed by the magnetic head. The nonvolatile memorystores a write current, a track pitch, a linear recording density and aflying height control heater power, selected such that the recordingdensity is maximum at each radius of the magnetic recording medium. Thecontroller as a first optimization means, derives, taking the writecurrent or the flying height control heater power as a write performanceadjustment parameter, a slope of a track average write performance withrespect to the write performance adjustment parameter at each of aplurality of radii of the magnetic recording medium. The controller alsostores in the nonvolatile memory a first set of fitting coefficients fora case in which the slope is approximated by a polynomial equation forthe radius of the magnetic recording medium. The controller, as a secondoptimization means, acquires the circumferential position dependence ofthe write performance at each of the plurality of radii of the magneticrecording medium, using the write current, the track pitch, the linearrecording density and the flying height control heater power stored inthe nonvolatile memory. The controller stores in the nonvolatile memorya second set of fitting coefficients obtained by approximating thecircumferential position dependence by a periodic function. Thecontroller, as a correction means, uses a track-averaged writeperformance change rate which is a function of the radius and iscalculated using the first set of fitting coefficients, and a localwrite performance function which is a function of the radius andcircumferential position and is calculated using the second set offitting coefficients, to correct the write performance adjustmentparameter at each of the radii and in each of circumferential positionsby subtracting a value of (local write performancefunction−track-averaged write performance)/track-averaged writeperformance change rate.

Further, a second mode of the invention is characterized in that, in thefirst mode, the write performance adjustment parameter is the writecurrent.

Further, a third mode of the invention is characterized in that, in thefirst mode, the write performance adjustment parameter is the flyingheight control heater power.

Further, a fourth mode of the invention is characterized in that, in anyone of the first through third modes, the degree of the radius r of thetrack-averaged write performance change rate is 3 or higher and 5 orlower.

By means of this invention, a magnetic reading and writing device can beprovided with a local write performance function to correct the writeperformance adjustment parameter (the write current or the flying heightcontrol heater power). The local write performance function is afunction of the radius and the circumferential position obtained byapproximating the circumferential position dependence of the writeperformance of a magnetic head for a magnetic recording medium. By thismeans, reading and writing optimization processing which also depends onthe circumferential position can be performed, without requiring theaddition of considerable resources compared with conventionaloptimization methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the magnetic reading and writing device of one embodimentof the invention;

FIG. 2 shows a controller of the magnetic reading and writing deviceaccording to one embodiment of the invention;

FIG. 3 shows a flying height control heater power dependence ofoverwriting;

FIG. 4 shows a circumferential position distribution of overwriting(prior to adjustment of the flying height control heater power bycircumferential position);

FIG. 5 shows a circumferential position distribution of the center trackremaining signal intensity for adjacent track erasure (prior toadjustment of the flying height control heater power by circumferentialposition);

FIG. 6 shows a circumferential position distribution of overwriting(after adjustment of the flying height control heater power bycircumferential position); and

FIG. 7 shows a circumferential position distribution of the center trackremaining signal intensity for adjacent track erasure (after adjustmentof the flying height control heater power by circumferential position).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, embodiments of the invention are explained in detail referring tothe drawings.

FIG. 1 shows the magnetic reading and writing device of one embodimentof the invention. A controller 1 controls a rotor 12 connected to amagnetic recording medium 6, issues reading and writing instructions toa code conversion/signal analysis device 3, exchanges data with anexternal interface, and similar, and in addition handles optimizationprocessing for the combination of a magnetic head 11 and the magneticrecording medium 6. Further, instructions to a head flying heightcontrol power supply 9 are output according to a read/write position. Innonvolatile memory 2, various types of information, including fittingcoefficients described below, are held. Examples of non-volatile memoryinclude read-only memory, flash memory, ferroelectric RAM, most types ofmagnetic computer storage devices (e.g. hard disks, floppy disks, andmagnetic tape), optical discs.

The controller 1 may be a general purpose computer or a dedicatedspecial purpose hardware item, and the optimization processing may beperformed by hard-wired logics or software/firmware stored in a memory.FIG. 2 shows one example configuration of the controller 1. Thecontroller 1 may include a bus 130 or other communication mechanism forcommunicating information and a processor 150 coupled with the bus 130for processing the information. The controller 1 also may include a mainmemory 110, such as a random access memory (RAM) or other dynamicstorage device (e.g., dynamic RAM (DRAM), static RAM (SRAM), synchronousDRAM (SDRAM), flash RAM), coupled to bus for storing information andinstructions to be executed by the processor 150. In addition, mainmemory 110 may be used for storing temporary variables or otherintermediate information during execution of instructions to be executedby processor. A storage device 120, such as a magnetic disk or opticaldisk, may be provided and coupled to the bus 130 for storing informationand instructions. This storage device is an example of a computerreadable medium, upon which the program may be encoded. The controller 1also may include input/output ports 140 to input signals to couple thecontroller 1. Such coupling may include direct electrical connections,wireless connections, networked connections, etc., for implementingautomatic control functions, remote control functions, etc. Suitableinterface cards may be installed to provide the necessary functions andsignal levels. The controller 1 also may include a communicationinterface 160 coupled to the bus 130. The communication interface 160may provide a two-way data communication coupling to a communicationlink 180 that may be connected to, for example, an external device 20.

The magnetic head 11 has a flying height control heater (not shown),recording head 5, and a reading element 7. The radial position of themagnetic head 11 is set by the magnetic head position locator 10according to an instruction issued by the controller 1. The magnetichead position locator 10 drives a voice-coil rotator of a magnetic headassembly (not shown) and locates the magnetic head 11 in a right radialposition.

A recording signal generation device 4 transmits signals for recordingto the recording head 5 based on instructions from the codeconversion/signal analysis device 3, and the recording head 5 performsmagnetic recording on the magnetic recording medium 6. Informationrecorded on the magnetic recording medium 6 is captured as signals viathe reading element 7. The captured signal, after passing through asignal amplifier 8, is sent to the code conversion/signal analysisdevice 3, where the recorded information is restored and is sent to thecontroller 1.

Below, the operation of the magnetic reading and writing device of thisembodiment is explained. In optimization processing, the controller 1performs various processing; at this time, the controller 1 can beviewed as means for executing the various processing.

First, as in conventional optimization methods, the controller 1performs optimization of the track pitch, linear recording density,write current, and flying height control heater power, with dependenceonly on the radial direction (step 101). By this means, the physicalformat is decided. The various values obtained by optimization arestored in the nonvolatile memory 2.

Next, at a plurality of radii, the track-averaged write performance isderived, when the flying height control heater power during writing isshifted, taking as the center the flying height control heater powerdecided by optimization in step 101 (step 102). This flying heightcontrol heater power is a parameter for adjusting the write performance,and is called the “write performance adjustment parameter”. FIG. 3 showsan example of measurement for perpendicular magnetic recording. Thehorizontal axis indicates the flying height control heater power duringwriting, centered on the flying height control heater power (mW)obtained by optimization depending only on the radial direction, and thevertical axis indicates, as a write performance evaluation value, the“overwrite”, defined as the ratio of the remaining intensity of ahigh-density recorded signal to the initial recorded signal intensitywhen low-density recording is performed after high-density recording.

The relation of FIG. 3 was fit to a first-degree equation, and the slopeΔf/Δp of the overwrite to the flying height control heater power pduring writing was derived (step 103). This was performed at eachradius, and fitting coefficients when approximating the slope Δf/Δp withrespect to the radius r by a polynomial equation were determined (step104). These values were stored in nonvolatile memory 2. These fittingcoefficients (corresponding to the “first set of fitting coefficients”)can be used at radius r to calculate the track-averaged writeperformance change rate (Δf/Δp)(r).

Next, at a plurality of radii, the optimization conditions of step 101for each radius are used to acquire the circumferential positiondependence of the overwrite (step 105). The solid line in FIG. 4indicates an example for a certain radius. Here, the horizontal axisindicates each of the directions when an entire circumference is dividedinto N=32 parts, and the vertical axis indicates the overwritecalculated only for that direction.

Further, this circumferential position dependence of the overwrite isfit to a periodic function, with one rotation as one period (step 106).That is, when the jth circumferential position overwrite measurementresults is f(j), this f(j) is approximated byf(j)=a(0)/2+Σ′a(k)cos(2πjk/N)+Σ′b(k)sin(2πjk/N)  (1).

Here Σ′ is the sum for values of k starting from 1. It is assumed thata(k)=(2/N)Σf(j)cos(2πjk/N) and b(k)=(2/N)Σf(j)sin(2πkj/N). Here Σ is thesum for values of j from 0 to N−1.

The broken line in FIG. 4 represents the result of approximation usingseven parameters from a(0) to a(3) and b(1) to b(3).

The above-described measurement and fitting are performed for aplurality of radii. Fitting coefficients a(k), b(k) at radius r=r(i) aredenoted by a(i,k) and b(i,k) respectively. The fitting coefficients whenthe relation between these coefficients a(i,k) and b(i,k) to r=r(i) isapproximated by a polynomial equation with respect to the radius r(corresponding to the “second set of fitting coefficients”) aredetermined (step 107). These values are stored in the nonvolatile memory2. On the basis of the stored fitting coefficients, functions a(r,k) andb(r,k) of the radius r are obtained.

Finally, shifts Δf(r,j) from the track averages at radius r andcircumferential position j of the local write performance functionf(r,j) expressing the local write performance is calculated, removingthe constant term in equation (1):Δf(r,j)=Σ′a(r,k)cos(2πkj/N)+Σ′b(r,k)sin(2πkj/N)  (2)(step 108).

The heater power p(r) optimized in the radial direction is modified toobtain the heater power for a direction j, p(r,j):p(r,j)=p(r)−Δf(r,j)/(Δf/Δp)(r)  (3)and actual recording is performed (step 109).

The radial-direction distribution is normally gentle, and so it isdesirable that the degree of the polynomial approximation not be madetoo high. For example, from 3 to 5 degrees or so is desirable. Thenumber of samplings exceeding (the number of polynomial equationdegrees+1) is sufficient.

Further, each of the above-described processing can be performed in anyorder, so long as ultimately the heater power p(r,j) can be corrected.

In the above explanation, the flying height control heater power duringwriting was used as the write performance adjustment parameter; but thewrite current may be used. With respect to minute changes, increasingthe flying height control heater power and increasing the write currentinduce similar actions. That is, there is the tradeoff that as the writeperformance is increased (and consequently the linear recordingdensities is raised), the write width increases (the track pitchworsens), and so the recording density is raised by performingoptimization which includes a dependence on the circumferentialposition, as described below.

In optimization by this method, high recording densities can be realizedas follows. In the magnetic reading and writing device shown in FIG. 1,FIG. 5 shows the results of measurement of the circumferential positiondependence of the remaining signal intensity at the original trackcenter, when a rectangular wave was recorded on a track sector, anderasure was then performed at a position distant by the track pitch fromthe track center. If this value cannot be maintained at a fixed value orhigher (generally approximately 80%), the signal recorded on theoriginal track cannot be correctly reproduced as a result of recordingon the adjacent track.

FIG. 6 and FIG. 7 respectively show the circumferential positiondependence of the overwrite and the circumferential position dependenceof the remaining signal intensity upon adjacent track erasure, uponperforming heater power adjustment during writing by angle according toequation (3). Specifically, the flying height control heater power ateach circumferential position was set, relative to the heater settingprior to adjustment, to a value reduced by(overwrite measured value at the circumferentialposition−circumferential position average value of overwrite)/1.6.

By means of the control indicated by equation (3), the circumferentialposition dependence not only of overwrite, but also of remaining signalintensity upon adjacent track erase is also reduced. In FIG. 7, thesolid line represents measurements at the track pitch, obtained as theresult using the conventional optimization method of step 101, and thebroken line represents measurements with the track pitch reduced to 95%.The broken line of FIG. 7 and the minimum values in FIG. 5 substantiallycoincide; this fact indicates that by means of the control of equation(3), 5% reduction of the track pitch (an increase by 5% in the trackdensity) is possible.

In this method, in addition to the optimization by radius of the priorart, control based on the angle, as well as storage capacity for thiscontrol, are necessary; but the data to be stored is only fittingcoefficients, requiring very little data storage, and no addition ofconsiderable resources over those used in conventional optimizationmethods is required.

As described above, by adopting this method to perform optimization, themargin accompanying the circumferential position distribution of writeperformance can be reduced when performing optimization, so that evenwhen optimizing for the combination of the same magnetic head andmagnetic recording medium, higher densities can be attained comparedwith conventional optimization methods.

What is claimed is:
 1. A magnetic reading and writing device,comprising: a magnetic head that performs a magnetic reading/writingupon a magnetic recording medium and a flying height control; acontroller that acquires dependence of write performance of the magnetichead on a variable representing each of a plurality of circumferentialpositions of the head with respect to the medium by measuring trackwrite performance with respect to the plurality of circumferentialpositions, and derives a set of fitting coefficients therefrom; and ahead flying height control power supply that adjusts an adjustmentparameter to control the flying height of the magnetic head according tothe circumferential position based upon the set of fitting coefficients.2. The magnetic reading and writing device according to claim 1, whereinthe set of fitting coefficients is a set of fitting coefficients of anequation comprising a periodic function that approximates a relationbetween write performance and the variable.
 3. The magnetic reading andwriting device according to claim 2, wherein the set of fittingcoefficients is a function of a radial position of the magneticrecording medium.
 4. The magnetic reading and writing device accordingto claim 3, wherein the function is a polynomial equation.
 5. Themagnetic reading and writing device according to claim 4, wherein thedegree of the polynomial equation is smaller than or equal to
 5. 6. Amagnetic reading and writing device, comprising: a magnetic head thatperforms a magnetic reading/writing upon a magnetic recording medium anda flying height control; a controller that acquires dependence of writeperformance of the magnetic head on a variable representing each of aplurality of circumferential positions of the head with respect to themedium by measuring track write performance with respect to theplurality of circumferential positions, and derives a set of fittingcoefficients therefrom; and a recording signal generation device thatadjusts an adjustment parameter to control a write current of themagnetic head according to the circumferential position based upon theset of fitting coefficients.
 7. The magnetic reading and writing deviceaccording to claim 6, wherein the set of fitting coefficients is a setof fitting coefficients of an equation comprising a periodic functionthat approximates a relation between write performance and the variable.8. The magnetic reading and writing device according to claim 7, whereinthe set of fitting coefficients is a function of a radial position ofthe magnetic recording medium.
 9. The magnetic reading and writingdevice according to claim 8, wherein the function is a polynomialequation.
 10. The magnetic reading and writing device according to claim9, wherein the degree of the polynomial equation is smaller than orequal to 5.